Ye-Shun Shen

A High-Capacity TH Multiple-Access UWB System With Performance Analysis

A flexible time-hopping (TH) multiple-access (MA) ultrawideband (UWB) system employing M-ary orthogonal pulse position modulation (PPM) is implemented and analyzed in this paper. In contrast to the conventional TH method using the fixed partition of TH slots, a new flexible TH scheme that utilizes the whole frame to carry out TH and PPM is proposed. The advantage of the proposed scheme is to increase the modulation level of PPM and improve the capability of MA. Based on the analytical CF technique, we also derive the probability distribution of the MA interference (MAI) and the average symbol error probability of the proposed scheme. Simulation results are provided to demonstrate the effectiveness of the proposed TH system and verify the analytical frameworks in both the additive white Gaussian noise (AWGN) channel and the realistic UWB fading channels. Irrespective of the adopted modulation level of PPM, the proposed TH system outperforms the conventional TH scheme. The tradeoff of the system parameters for the proposed TH system under the constraints of fixed bit rate and signal bandwidth is also examined.

An Accurate Performance Analysis of Hybrid TH/DS Multiple Access UWB System Using N-ary Biorthogonal PPM

A hybrid time-hopping/direct-sequence (TH/DS) multiple access ultra-wideband (UWB) system combined with N-ary biorthogonal pulse position modulation (BPPM) is proposed and analyzed. Based on the exact characteristic function (CF) technique, we also derive the probability distribution of the multiple access interference (MAI) and the average symbol error rate (SER) of the proposed scheme. Simulation results are provided to verify the analytical frameworks. The tradeoff of the system parameters for the proposed system under the constraints of fixed bit rate and signal bandwidth is also examined.

A New SAGE-Based Receiver for MC-CDMA Communication Systems

Abstract Multicarrier code division multiple access (MC-CDMA) systems have arrested a lot of attention, owing to the simple implementation and powerful resistance to frequency-selective channels and the CDMA with the suitability for multiuser systems. Although MC-CDMA systems spread symbols using orthogonal codes to ensure orthogonality, orthogonality may be destroyed at the receiver due to frequency selective fading and then results in multiple access interference (MAI) and inter-carrier interference (ICI). The space-alternating generalized expectation–maximization (SAGE) algorithm is with high convergence speed and performs maximum-likelihood estimation/detection of the transmitted signals. For MC-CDMA systems, existing SAGE algorithm is used to cancel the ICI (Panayirci et al. in IEEE Trans Signal Process 58(8): 4225–4238, 2010), or to cancel the MAI (Panayirci et al. in 16th IST Mobile and Wireless Communications Summit, 2007). In this paper, the proposed interference cancellation scheme not only performs MAI cancellation but also performs ICI cancellation for the MC-CDMA systems. Some simulation examples are given to show the effectiveness and comparisons of the proposed receiver.

A performance analysis of the high-capacity TH multiple access UWB system using PPM

A time-hopping (TH) multiple access ultrawideband (UWB) system combined with a large modulation level of M-ary pulse position modulation (PPM) is considered and analyzed. Unlike the conventional TH method that the number of the provided TH slots becomes fewer as the adopted modulation level of M-ary PPM is lager and the data rate is fixed, a feasible TH scheme that utilizes the whole frame duration to carry out TH and PPM is proposed in the paper. The advantages of proposed TH system are to use the large modulation level of PPM, reduce the effect of the multiple access interference (MAI) and increase multiple access capability. The characteristic function (CF) of the MAI for proposed sytem is derived to obtain the probability density function of MAI and average symbol error rate. The simulation results of the proposed TH system are provided to verify the analytical results and show the performance improvement over the conventional TH and DS UWB systems.

N-Ary Biorthogonal Pulse Position Shape Modulation for Hybrid TH/DS Multiple Access UWB System

A N-ary biorthogonal pulse position shape modulation (BPPSM) for hybrid time hopping/ direct sequence (TH/DS) multiple access ultrawideband (UWB) system is proposed and analyzed in this paper. The characteristic function (CHF) of the multiple access interference (MAI) is derived and, accordingly, the average symbol error rate (SER) of the proposed system can be accurately evaluated. Simulation are carried out to verify the analytical results in additive white Gaussian noise (AWGN) channel and to illustrate the system performance in realistic UWB fading channels. As increasing the number of adopting pulses, the proposed TH/DS Nary BPPSM system can provide better SER performance compared with the TH/DS Nary BPPM scheme. Given the constraints of fixed bit rate and signal bandwidth, the impact of adjusting various system parameters on the system performance is also investigated.

Performance analysis of a TH/DS N‐ary BPPM UWB system

A hybrid time-hopping/direct-sequence (TH/DS) multiple access ultra-wideband (UWB) system using N-ary biorthogonal pulse position modulation (BPPM) is proposed and analysed in this paper. Based on the analytical characteristic function method, we derive the accurate probability distribution of the multiple access interference and calculate the average symbol error rate (SER) of the proposed system. Simulation results are provided to verify the analytical frameworks in additive white Gaussian noise channel and to illustrate the system performance in realistic UWB fading channels. The proposed TH/DS N-ary BPPM system is shown to provide better SER performance compared with that of the conventional TH M-ary PPM scheme. We also investigate the trade-off of the proposed system parameters with fixed bit rate and fixed signal bandwidth. Copyright

A new time-hopping/direct-sequence biorthogonal PPM UWB communication system

In order to increase the capacity and diminish the multiple access interference (MAI) of an ultra-wideband (UWB) system, we propose a new time-hopping/direct-sequence (TH/DS) scheme using N-ary biorthogonal pulse position modulation (BPPM). In contrast with the conventional TH/DS systems employing fixed partition of the TH slots (Shen and Ueng, Proceedings of the IEEE VTC-Spring, 2010), the proposed TH/DS system can put the start location of the TH slot in any one of Q available pulse positions within the frame. In the proposed TH/DS system, the modulation level of BPPM can be increased and the multiple access capability can be improved without degrading the system performance. Compared with the existing TH-UWB system that employs the whole frame to carry out TH process (Shen et al. IEEE Trans. Veh. Technol. 59(2), 742-753, 2010), the proposed system has the merits of smooth power spectral density and low receiver complexity. In this article, we also derive the probability distribution of MAI for each correlators output of the proposed TH/DS system based on the analytic characteristic function technique. In order to verify the correctness of the performance analyses and to demonstrate the effectiveness of the proposed TH/DS system, some simulation results are given in both the additive white Gaussian noise channel and the realistic UWB fading channels. From the simulation results, we find that the proposed TH/DS system outperforms the conventional TH/DS scheme.

Performance analyses of adaptive noncoherent receivers for MC-CDMA communications

In this paper, we propose differential phase-shift keying DPSK noncoherent receivers for multicarrier code division multiple access systems in multipath channels. The noncoherent receivers are composed of a linear equalizer and a decision-feedback differential detector to detect DPSK signals. The performances of the proposed noncoherent receivers can be improved by increasing the number of feedback symbols. For an infinite number of feedback symbols, the optimum weight can be derived analytically, and the performances of the proposed noncoherent receivers approach that of the conventional coherent receiver. For adaptation of the equalizer coefficients, modified least mean square and recursive least squares algorithms are proposed. Furthermore, the reduced-rank schemes are proposed to simplify the system complexities. Some simulation examples are given to show the system performances of the four proposed receivers. Copyright

Blind receiver for MIMO SC-FDMA communications

Because SC-FDMA (Single Carrier Frequency Division Multiple Access) is with the desirable characteristics of OFDMA and the low PAPR (Peak-to-Average Power Ratio) of single-carrier transmission schemes, it has been adopted as the uplink transmission scheme in 3GPP LTE to approach the demand for data transmission rates and error performance. By combining multiple-input multiple-output (MIMO) techniques with the SC-FDMA modulation scheme, MIMO SC-FDMA systems can achieve high data rates over broadband wireless channels. In this paper, we propose the iterative multiuser detection scheme for the low-density parity-check (LDPC) coded MIMO SC-FDMA communication systems. Some simulation examples for uplink scenario are given to demonstrate the effectiveness of the proposed schemes.

Adaptive constrained CM-based multicarrier-CDMA receivers in multipath fading channels

Two blind adaptive receivers, based on constrained constant modulus (CM) algorithms, are investigated for the detection of the multicarrier code division multiple access (MC-CDMA) system in the multiuser and multipath channels. As the data rate of the information bit is getting high enough, the transmitted signal of the MC-CDMA system becomes more sensitive to the frequency-selective fading. To mitigate this drawback, the parallel transmissions of multiple data symbols within one OFDM block are employed in the proposed systems to ensure that the length of the cyclic prefix (CP) is longer than the delay spread of the multipath channel. The first receiver is called a full-tap receiver (TDes receiver), which can carry out the interference suppression in the frequency-domain. Alternatively, a reduced-tap receiver (TRTap) is proposed on the basis of the derived cyclically shifting matrix. According to the derived matrix representation of the received signal, the analytical steady-state mean square errors (MSEs) for both receivers are also derived and compared. Simulation results are provided to illustrate the effectiveness of the proposed receivers and validate the accuracy of the theoretical analysis. As expected, the symbol error rate (SER) performance of the full-tap receiver is better than that of the reduced-tap receiver in severe interference environments. In contrast, the reduced-tap receiver can provide the satisfied SER performance just like the full-tap receiver in low-interference scenarios, even though the former one adopts only one-tap equalization.